A NACA duct is a common form of low-drag intake design, originally developed by the National Advisory Committee for Aeronautics during the 1940s. In particular, a NACA duct is a flush mounted inlet or scoop that is commonly used to supply cooling, ventilation, or combustion air to the mechanical systems of air and land vehicles. Since the NACA duct is a depression in the body's surface, as opposed to a traditional scoop that protrudes outside the body, the duct produces less drag. However, a disadvantage of such a configuration is that, since the duct does not reach out into the high energy air farther away from the body, a large proportion of low energy boundary layer air, i.e., the layer of air that clings to the surface or a moving body, is drawn in which reduces the effectiveness of the duct. NACA ducts partially counteract this disadvantage by incorporating certain geometric features. For example, a NACA duct consists of a ramp that gently slopes downward into the body. In addition, the ramp is narrow at its leading edge, but widens dramatically at its trailing edge. The increasing width is bounded by vertical or near-vertical side walls that have a characteristic reflex curvature. These S-shaped walk are a defining characteristic of the NACA duct and are believed to generate a pair of counter-rotating vortices that efficiently draw higher energy air from outside the boundary layer into the duct.
Race cars designers typically employ NACA ducts on lateral surfaces of the both to draw in air for less demanding applications such as ventilation or cooling. Aeronautical engineers employ NACA ducts on various types of aircraft for similar purposes. Applications such as combustion that require large volumes of high energy air are usually best served by conventional protruding scoops on the lateral surfaces of the body or inlets on the front-facing surfaces.
The shape and depth change of the duct are critical for proper operation. When properly implemented, it allows fluid (usually air) to be drawn into an internal duct, with a minimal disturbance to the flow or increase in drag.
Golf ball dimples work by inducing turbulence in the boundary layer of the air adjacent to the surface of the golf ball. Compared to laminar boundary layers, turbulent boundary layers are better able to remain attached to the ball surface. Thus, the size of the wake behind the golf ball can be reduced if the boundary layer is turbulent rather than laminar, resulting in a reduction of pressure drag acting on the golf ball. Although turbulent boundary layers generate greater skin friction drag, this is dramatically outweighed by the reduction of pressure drag. However, manufacturers are still dedicated in their efforts to reducing pressure drag and minimize the corresponding increase in skin friction drag to maximize the net benefit. Accordingly, there is a need in the art for improved dimple designs and geometry that induce turbulence in the boundary layer by drawing the air flow into the dimples. The present invention relates to such dimple designs and geometry.